Setting up a clash between counter-terrorism priorities and constitutional protection against unwarranted intrusion, three top federal law enforcement officials urged Congress and Silicon Valley to provide government agencies special access to encrypted cellphones and other Internet devices.

The pitch Wednesday came amid renewed concern about American vulnerabilities as a cascading series of coincidental computer malfunctions briefly grounded United Airlines aircraft and brought the New York Stock Exchange and other high-profile digital networks to a halt.

Testifying before two Senate committees, FBI Director James B. Comey warned that without legal access to encrypted emails, texts and other communications, "we may not be able to identify and stop terrorists who are using social media to recruit, plan and execute an attack in our country."

Even with a warrant, FBI investigators often can't read encrypted text messages and are unable to open locked files stored on computers. Companies such as Google and Apple have built encryption into messaging software.

The FBI wants Congress and the industry to come up with a solution. Comey expressed disbelief Wednesday that Silicon Valley companies couldn't develop secure encryption methods that also allowed companies to use a backdoor key when served with a warrant.

"I don't exactly know where the great demand for this is coming from," Comey said of encrypted devices. "I don't know ordinary folks who say, 'I want a phone that can't be opened.'"

Encryption technology has been embraced by civil liberties groups and others who want to keep the government out of private communications. Public concern has grown since former National Security Agency contractor Edward Snowden disclosed numerous government efforts to access emails and other digital systems at home and abroad.

Deputy Atty. Gen. Sally Quillian Yates warned that if encrypted devices and communications remained off-limits, "we are creating safe zones where dangerous criminals and terrorists can operate and avoid detention."

Lawmakers should not risk the real economic, geopolitical and strategic benefits of an open and secure Internet for law enforcement gains that are at best minor and tactical.— Top American cryptographers, in a letter to FBI Director James Comey

Homeland Security Secretary Jeh Johnson, in a speech to a Washington think tank, called for more efforts to protect crucial digital networks from destructive cyberattacks.

"To be frank, our federal cybersecurity is not where it needs to be," he said at the Center for Strategic and International Studies, noting the recent hack of security background checks and millions of other files at the federal Office of Personnel Management.

He urged Congress to help protect companies who report cyberattacks from liability, and to create a national standard for reporting data breaches.

On Tuesday, the nation's top cryptographers sharply objected to any government demands for companies to alter their technology to allow law enforcement to secretly see what Americans are sending and receiving.

"Lawmakers," the scientists and engineers warned in a letter to Comey, "should not risk the real economic, geopolitical and strategic benefits of an open and secure Internet for law enforcement gains that are at best minor and tactical."

Some Silicon Valley and other California lawmakers strongly oppose any law enforcement intrusion into personal Web activities.

The House has twice voted against allowing law enforcement access, and Sen. Charles E. Grassley (R-Iowa) acknowledged Wednesday at a Senate Judiciary Committee hearing that no new legislation was pending.